Bitumen and heavy crude oil are characterized by high viscosity and low American Petroleum Institute (API) gravity. These characteristics result in higher costs for extraction, gravity separate sand, transportation, and refining than the costs associated with conventional light crude oil.
Bitumen, defined as an API Gravity less than 10 degrees, and heavy crude oil are the remnants of very large volumes of conventional light crude oils that have been generated and degraded, principally by bacterial action (Speight, J. 1999). Bitumen and heavy crude oil, chemically and texturally resemble the residual generated by refinery distillation of crude oil. The resource base of bitumen and heavy crude oil is immense and not a constraint on the expansion of production. These resources can make an important contribution to future oil supply if they can be extracted and transformed into usable refinery feedstock at sufficiently high rates and at costs that are competitive with alternative methods. Another possible heavy petroleum reserve is the four tar lakes in the world. The Guanaco Lake in Venezuela is slated to be harvested for removal of its estimated 75 million barrels of tar.
Bitumen and Heavy Crude Oil
The total in-place heavy crude oil and bitumen is greater than the original light crude oil in place in the world's known conventional oil fields. The methods used in the commercially successful projects in Venezuela Orinoco Oil Belt, for extraction of heavy crude oil, and Canada's Alberta, for bitumen, are proven production strategies and technologies that are being considered for smaller deposits elsewhere. The commercial value achieved in these locations is likely to lead to exploration that could result in additional deposits and verification of larger resource volumes at identified deposits.
Outside of Canada, 367 bitumen deposits are reported in 22 other countries. The largest volumes of bitumen after Canada are in Kazakhstan and Russia: both countries are well endowed with less cost of extraction conventional crude oil. The worldwide volumes of discovered bitumen are 2,511 billion barrels.
According to the International Energy Agency (IEA), the estimated volumes of heavy crude oil worldwide are about 6 trillion barrels, of which 2.5 trillion barrels are in Canada, 1.5 trillion barrels are in Venezuela, 1 trillion barrels are in Russia and 100 to 180 billion barrels are in the USA. The recovery of heavy crude oil is commonly practiced in countries such as USA, Canada and Venezuela. Heavy oil is recorded in 162 deposits located in 21 countries. A map of a major heavy crude oil deposits, the Orinoco oil belt in the Eastern Venezuela basin, is shown in FIG. 1. Heavy crude oil production accounts for more than 20% of Venezuela's oil production. Some fields are comprised only of heavy crude oil reservoirs whereas other such reservoirs occur in fields producing mainly from conventional light and intermediated crude oil reservoirs.
Venezuela blends its crude oil to produce and to export products, one tests to API of 30 degrees and is refinery ready, and the other, Merey-16, tests to an API of 16 degrees. The Merey-16 sells at ten dollars less per barrel than the API gravity of 30 degrees.
Characteristics of Crude Oil
No crude oil has ever been completely separated into its individual component chemicals. For example, a total of 141 component chemicals were identified in one sample of crude oil from Oklahoma. But these compounds only accounts for 44% of the total individual component chemicals in the crude. The component chemicals in crude oil are classified into paraffinic, aromatic and napthenic groups (Speight, J. 1999). Paraffin hydrocarbons are characterized by open or straight chains of carbons, joined by single bonds. The first four paraffin hydrocarbons are: methane, ethane, propane and butane. The isomers of these compounds, contain branched chains, are also paraffins. The first four members are gases at room temperature and pressure. Compounds ranging from pentane (C5H12) through heptadecane (C17H36) are liquids, while the heavier members are colorless, wax-like solids. Unsaturated hydrocarbons, with one or more double or triple bond between the carbons, consist of olefins, diolefins, and acetylenes. These compounds are highly reactive and are not normally present to any great extent in crude oil. Naphthene hydrocarbons are ringed molecules and are also called cycloparaffins. These compounds, like the paraffins, are saturated and very stable and make up the second primary constituent of crude oil. Aromatic hydrocarbons, derivatives of benzene, are also cyclic. The rings are characterized by alternating double bonds and, in contrast to olefins, are quite stable, though not as stable as paraffins. Crude oils are complex mixtures of these hydrocarbons. Oils containing primarily paraffin hydrocarbons are called paraffin-based or paraffinic. Naphthenic-based crudes contain a large percentage of cycloparaffins in the heavy components. Highly aromatic crudes are less common but are still found around the world. Crude oils tend to be a mixture of aromatic compounds of paraffin and naphthene, with paraffins and naphthenes the predominant species.
Paraffinic Asphaltenes in Crude Oil
Asphaltenes, present in crude oil, are the black color components of relatively high-molecular-weight that are characterized as polar, polycyclic, aromatic ring compounds. Pure asphaltenes are nonvolatile, dry, solid, black powders. Asphaltenes do not dissolve in crude oil but exist as a colloidal suspension. They are partially soluble in aromatic compounds such as xylene, but will precipitate in the presence of light paraffinic compounds such as pentane or naphtha.
FIG. 2 compares and contrasts the chemical composition, based on number of carbons in the compounds, of natural gas and crude oil and further identifies tars and its subset asphaltenes in the crude oil. While not totally definitive, it can be observed that heavy crude oils, with lower API gravities, tend to be more naphthenic, while light crude oils, with higher API gravities tend to be more paraffinic. This is illustrated in FIG. 2 by an arrow to the right that indicates that heavy crude oil contains more naphthenic hydrocarbon compounds and an arrow to the left indicating the light/intermediate crude oil contains more paraffinic hydrocarbons compounds.
One of the main challenges associated with production of heavy crude oil is transportation of the oil by pipelines, particularly without the prior reduction of the oil viscosity to acceptable levels to ensure oil fluidity in pipelines. Light crude oil, or one of its distillates, such as naphtha, heavy naphtha or kerosene, or diesel is used as a blend stock to reduce the viscosity and thus increase the API gravity of heavy crude oil. In one example, the viscosity of heavy crude oil was reduced from 4,000 to 500 cSt: an 88% reduction. However, delayed asphaltene precipitation (DAP) is often associated with blending. One blending formula effective in reducing the viscosity of heavy crude oil, without resulting in DAP, is 0.5 to 2.0 weight percent of a mixture of n-hexane and toluene. There is a need to deconstruct the asphaltene to liberate its n-hexane and toluene fractile building blocks and allow these compounds to migrate into the general population of compounds to reduce the viscosity of the crude oil, allowing pipeline transport, and avoiding the complexities/cost of purchasing these compounds for blending of the internally generated compounds that are superior to blending with heavy naphtha or other distillates that produce harmful DAP.
Specific Gravity (SG) as a Function of API Gravity
The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water: if the API gravity of a crude oil is greater than 10, it floats on water; if it is less than 10, it is heavier and sinks. API gravity values of most petroleum liquids fall between 10 and 70 degrees. The formula to calculate API gravity from a known specific gravity (SG) is:
      API    ⁢                  ⁢    Gravity    =            141.5      SG        -    131.5  
Conversely, the SG of petroleum liquids can be derived from known API gravity value as:
            SG      ⁢                          @                          ⁢      60        ⁢                  ⁢          °F      .        =      141.5                  API        ⁢                                  ⁢        Gravity            +      131.5      
Thus, a heavy crude oil with a specific gravity of 1.0, with the same density as pure water at 60° F., has an API gravity of 10. The following table contains the SG @ 60° F. for specific petroleum liquids at incremental API degrees.
API DegreesSpecific Gravity 11.0680 51.0370 81.0140101.0000150.9659200.9340250.9042300.8762350.8498400.8251450.8017500.7796550.7587600.7389700.7022800.6690900.6388Kinematic Viscosity as a Function Specific Gravity (SG)
Centistokes (cSt), are the units for measurement of the kinematic viscosity, which is the absolute viscosity, measured in centipoise (cP) of the petroleum divided by the SG.Kinematic Viscosity (cSt)=Absolute Viscosity (cP)/Specific Gravity
Since most crude oil have SG between 0.8 and 1.0, the value of absolute viscosity (cP) is often smaller than the value of the kinematic viscosity (cSt).
Asphaltene
Petroleum engineers harbor the assumption that asphaltene constitutes a colloidal size fraction of dead, unavailable as petroleum liquid, fraction of crude oil: like suspended fine solids. This leads to the persistent generalization that the decrease in API gravity is a function of the increase in the crude oil's asphaltene content (Buckley and Wang, 2002).
The following equation for SG as a function of asphaltene content in grams per liter was derived by fitting a line to the physical chemical data for 500 plus crude oil samples.SG=0.78+0.0054×C0.61                 Where: C is the asphaltene content of the crude oil in grams per liter Conversely, the asphaltene content of the crude oil can be derived from their API gravity value as:        
      Asphaltene    ⁢                  ⁢    Content    ,            g      ⁢              /            ⁢      l        =                            (                      SG            -            0.78                    )                0.0054            0.61      API, Specific Gravity, Viscosity and Asphaltene Content
The physical chemical characteristics of a Venezuelan heavy crude oil for Block C North are as follows: API Degrees is 8 @ 60° F., Absolute Viscosity is 5,000 (cP) @ 100° F., and Transportation Temperature is 180° F. The maximum viscosity to allow crude oil to be transported is a kinematic viscosity between 250 to 400 cSt: depending on the pipeline. The assumption is made that the heavy crude requires heating to 180° F. to be moved and this corresponds to a kinematic viscosity of 400 cSt. Therefore, the following calculations can be made:
                    ⁢                  API        ⁢                                  ⁢        Degrees        ⁢                                  ⁢        of        ⁢                                  ⁢        8            =              Specific        ⁢                                  ⁢        Gravity        ⁢                                  ⁢        of        ⁢                                  ⁢        1.014                                Kinematic        ⁢                                  ⁢        Viscosity        ⁢                                  ⁢                  (          cSt          )                    =                        5          ⁢                      ,                    ⁢          000          ⁢                                          ⁢          cP                          4          ⁢                      ,                    ⁢          931          ⁢                                          ⁢          cSt                      ,          Absolute      ⁢                                        ⁢                                      ⁢              Viscosity        /        1.014              ,          SG      =                          ⁢                          ⁢              Asphaltene        ⁢                                  ⁢        Content              ,                  g        ⁢                  /                ⁢        l            =                                                  (                              SG                -                0.78                            )                        0.0054                    0.61                =                  17.1          ⁢                                          ⁢          g          ⁢                      /                    ⁢          l                    
The kinematic viscosity of 400 cSt is required to move the crude. This is obtained, as stated above, by heating to 180° F. The proposed in the present invention is a treatment that allows the movement of the crude at a lower temperature by changing the chemical composition of the crude and has the potential, at sufficient dosage, to allow movement of the crude at ambient temperature and obtain an API of sufficient large value to allow the crude to be “refinery ready”.
Steam Injection for Enhanced Oil Recovery and Chemicals as Supercritical Fluids
The most common thermal technologies used for enhanced oil recovery of heavy crude oil are steam flood and cyclic steam stimulation (Alboudwarej, H., 2006).
The steam flooding process involves steam injection through injection wells to an oil reservoir. The areas around the injection wells are heated up to steam temperature. The steam front starts condensing to hot water which still conducts heat to the system, at lower level than steam, and drives oil toward production wells. The process becomes more efficient if thermal communications are established between the injection and production wells. The oil production, then, becomes more fluent as its viscosity is significantly reduced.
Cyclic steam stimulation, also known as “huff-and-puff” involves the injection of steam into a reservoir for some time and then shutting in the well for sufficient time. This enables steam to soak, and therefore, heats the reservoir and mitigates oil mobility. After some time, the well is allowed to flow and production is resumed. This process may be repeated for several times until production of certain volumes of injected fluid or the reservoir pressure is decreased.
The conditions of down well steam injection achieve temperatures and pressure conditions that transform solvent chemicals into supercritical fluids: because these conditions are above the critical point for these materials. The distinct liquid and gas phases do not exist above the critical point as shown in the following table.
DensityViscosityDiffusivity(kg/m3)(μPa · s)(mm2/s)Gases110 1-10Supercritical 100-1000 50-1000.01-0.1 FluidsLiquids1000 500-10000.001
The solvent effuses through the solids like a gas and dissolves materials in the asphaltene like a liquid. The extraction of the aromatic and alkane chain carbon materials from the asphaltene occurs at an accelerated rate due to the low viscosity and high diffusivity associated with supercritical fluids. The following table contains critical temperature characteristics for some solvent chemicals.
MolecularCriticalCritical Critical weighttemperaturepressuredensitySolventg/molKMPa (atm)g/cm3Carbon dioxide (CO2)44.01304.17.38 (72.8)0.469Oxolane (CH2)4O72.15415.19 (51.2)Methanol (CH3OH)32.04512.68.09 (79.8)0.272
Two factors have made light crude less available over the decades. First, light crude was the first crude and second the demand for light crude to blend with heavy crude and bitumen is accelerating the demand of light crude oil: as these reserves are becoming a larger part of our petroleum supply. There is a need for an alternative to blending light crude with heavy crude and bitumen. If this alternative was a derivative of vegetable oil then it would be renewable and practically inexhaustible and would lessen the current high demand for light crude oil: allowing heavy crude and bitumen to have unrestricted access as a source for the world's petroleum supplies.